Majority of current tumor management approaches are related to surgical means. Surgical treatment of cellular tissues usually exposes both the target and surrounding tissues to substantial trauma and the procedure is costly and time consuming. During a surgical procedure, precise placement of a treatment apparatus is difficult because of the specific location of a target tissue in the body or the proximity of the target tissue to obstructions or easily damaged critical body organs, such as nerves and blood vessels. In the past few years, new products with an emphasis on minimally invasive approaches are being progressively developed to replace the traumatic nature of traditional surgical procedures.
There has been a relatively significant amount of development activity in the field of high energy as a tool for treating tumors. It is known that elevating the temperature of tumors is helpful in the treatment and management of cancerous tissues. The mechanisms of selective cancer cell eradication by high energy doses are not completely understood. However, Edwards et al. in U.S. Pat. No. 5,536,267 hypothesized certain cellular effects of high energy on cancerous tissues. Nevertheless, treatment methods for applying heat to tumors include the use of direct contact radio-frequency (RF) applicators, microwave radiation, inductively coupled RF fields, ultrasound, laser, and a variety of simple thermal conduction techniques.
In the last few years, high frequency currents were used in electrocautery procedures for cutting human tissues, especially when a bloodless incision is desired or when the operating site is not accessible with a normal scalpel but presents an access for a thin instrument through natural body openings such as the esophagus, intestines, uterus, or urethra. Examples include the removal of prostatic adenomas, bladder tumors or intestinal polyps. In such cases, the high frequency current is fed by a surgical probe into the tissue to be cut. The resulting dissipated heat is controlled so that no boiling and vaporization of the cell fluid occurs at this point. The frequency of the current for this use must be above ca. 300 kHz in order to avoid any adverse effect such as nerve and/or muscle responses.
Destruction of cellular tissues in situ has been used in the treatment of many diseases and medical conditions alone or as an adjunct to surgical removal procedures. It is often less traumatic than surgical procedures and may be the only alternative where other procedures are unsafe or unavailable. Ablative treatment apparatus has the advantage of using a destructive energy which is rapidly dissipated and reduced to a non-destructive level by conduction and convection forces of natural body process. Ablative energy may also be controlled by a close-loop temperature sensing and control mechanism.
The same is true for ablation of the tumor itself through the use of RF energy. Different methods have been utilized for the RF ablation of masses such as tumors. Instead of heating the tumors it is ablated through the application of RF energy. This process has been difficult to achieve due to a variety of factors, such as access site, probe location, electrode positioning and energy level. Among them, the most critical factor is the positioning of the RF ablation electrode to effectively ablate all of the mass by controlled delivery and monitoring of RF energy to achieve successful ablation without damage to the surrounding healthy tissue. An ablation apparatus with ultrasonic imaging capabilities meets the positioning requirements.
There have been a number of different treatment methods and apparatus for minimally invasively treating tumors. One such example is an endoscope that produces RF hyperthermia in tumors, as described in U.S. Pat. No. 4,920,978. In U.S. Pat. No. 4,920,978, an endoscope for RF hyperthermia is disclosed. In U.S. Pat. No. 4,565,200, an electrode system is described in which a single entrance tract cannula is used to introduce an electrode into a selected body site. In U.S. Pat. No. 5,458,597, an RF probe with fluid infusion capability is described. Similarly, in U.S. Pat. No. 5,536,267, a multiple electrode ablation apparatus with fluid infusion means is disclosed. For the system with a close-loop temperature control mechanism, the fluid infusion means for the sole purpose of cooling-off the tissues may not be required. Recent clinical studies have indicated that RF energy is rapidly dissipated and reduced to a non-destructive level by conduction and convection forces of natural body process. In all examples, the tissue destruction energy and/or substances have been used to destroy malignant, benign and other types of cells and tissues from a variety of anatomic sites and organs. Tissues treated include isolated carcinoma masses and target tissues in organs such as prostate, glandular and stromal nodules characteristic of benign prostate hyperplasia.
After the exact location of a target tissue is identified, the ablation apparatus may still not easily approach the target site even with assistance of an internal viewing means, such as an endoscope. This viewing situation may turn into a nightmare when an endoscope approach becomes prohibitive or unavailable during procedures. An external ultrasonic imaging capability therefore becomes in need so that ablation is not taking place in an inappropriate location.
In the U.S. Pat. No. 4,794,931, there has been disclosed a catheter apparatus and system which can be utilized for ultrasonic imaging. However, there is no disclosure to how such an apparatus and system can be utilized in conjunction with a tissue ablation apparatus to achieve the desired ultrasonic imaging. In U.S. Pat. No. 5,409,000, an endocardial mapping and ablation system with ultrasonic imaging capabilities is disclosed. However, there is no disclosure to how such a system can be utilized in tissue ablation which is anatomically different from an endocardial ablation.
There is therefore a need for an RF ablation apparatus with ultrasonic imaging capabilities that is useful for treatment and reduction of undesired body tissues by minimally invasive procedures. It would be desirable for such an apparatus to surround the circumferential base of a tumor via ultrasonic imaging and comprising treatment electrodes to define a controlled ablation amount of RF energy by monitoring the temperature and controlling the energy delivered. Additionally, there is a need for an ablation apparatus with a sharp edge electrode to loosen the target tissue for improved ablation treatment. This would provide for the most effective method for reducing the mass of any type of tissue containing tumor cells and the like.